Year	Percent
1991	49.08
1992	48.99
1993	45.98
1994	45.01
1995	44.41
1996	43.27
1997	42.98
1998	43.59
1999	45.37
2000	45.77
2001	45.98
2002	46.03
2003	46.74
2004	46.48
2005	46.54
2006	46.77
2007	46.63
2008	46.1
2009	44.97
2010	44.86
2011	45.16
2012	45.91
2013	46.77
2014	49.51
2015	51.09
2016	52.91
2017	53.91
2018	54.46
2019	54.88
2020	54.25